It is well known that improper automobile tire inflation causes accelerated and uneven tire wear, and increases the risk of tire blow outs which, in turn, presents a traffic safety hazard. Such problems can often be eliminated by monitoring of the tire's pressure and, accordingly, by inflating the tire to the proper pressure.
Many prior methods and apparatus for measuring automobile tire pressure are known. Such prior devices are generally of three types, namely: (1) a detached pressure gauge which may be temporarily connected to the valve stem of a non-moving tire for purposes of reading tire's pressure; (2) a remote-reading gauge system that has a pressure sensing device that constantly senses tire pressure in communication with a remote indicator (typically in the automobile's dashboard), which allows either constant or intermittent tire pressure monitoring from inside the automobile; and (3) a tire pressure gauge or indicator permanently attached to the tire's valve stem by which the tire pressure can be read directly when the tire is not moving.
Of the third type, prior pressure gauges that are arranged in permanent communication with a tire's valve stem typically either have the indicator component mounted at or near the valve stem, itself, or have the indicator component located at or near the center of the wheel. In the latter instance, there is typically a pneumatic conduit running between the valve stem and the indicator component.
There are several problems with prior devices in which the indicator component is mounted at the valve stem or near the valve stem (for example, mounted on the rim of the wheel). Such devices are inherently unbalanced, since there is typically nothing counterbalancing the eccentric weight of the off-center indicator component. In addition, because these prior devices are off-center (relative to the tire's and the automobile's axle), they must be designed to endure high centrifugal forces which may be encountered when the automobile moves and the wheel turns. Such high forces can be destructive to the device as well as to the automobile. In addition, in the event the device becomes detached from the valve stem while the automobile is in motion, the device may become a high velocity projectile and thus present a safety hazard. Additionally, because of the eccentricity of the load that these devices add to the tire, the automobile's tire may become unbalanced, thus presenting a safety problem and causing an uneven tire wear and an unsafe ride for the automobile's passengers. Also, in order to minimize the effects of the large eccentric load, such prior devices are typically designed to be very small—often too small for the gauge itself to be easily read by an operator.
In order to overcome some of the problems caused by eccentric loading of stem-mounted or wheel rim-mounted air pressure gauges, some prior devices have been designed having the pressure indicator component mounted at the center of the wheel, typically on the hub. In such prior devices a pneumatic conduit typically is removeably attached at one end to the tire's valve stem; and the other end is permanently attached to the pressure indicating gauge component. U.S. Pat. No. 4,953,395 is an example of this type of wheel-mounted pressure gauge.
Although such prior devices offer advantages over valve stem-mounted and wheel rim-mounted pressure gauges, such prior devices are still often unbalanced, owing principally to the eccentric load of the valve stem, itself and the conduit attached to it.
Another problem of such prior hub-mounted pressure gauges is that attachment of the gauge member is typically accomplished by the addition of bolts and nuts, which can add cost, weight and eccentric loads to the wheel system.
Another problem of such prior devices is that, in order to add air to the tire, either the conduit needs to be removed from the valve stem or, alternatively, the valve stem needs to be fitted with a special supplemental valve port.